1. Field of the Invention
The present invention relates to automotive heat exchangers having inlet and outlet header pipes and a number of parallel tubes extending between the inlet and outlet header pipes to provide parallel flows of coolant between both of the header pipes.
2. Description of the Prior Art
The well-known parallel flow type heat exchangers, such as condensers for automotive air conditioners, include inlet and outlet header pipes and a number of flat tubes extending in parallel between the two header pipes.
In such heat exchangers, the flat tubes are connected to the header pipes by, as FIG. 7 shows, inserting each tube 23 into an insertion opening 22 of a header pipe 21 which has a circular cross-section (see Japanese Patent Application Kokai No 63-34466) or, as FIG. 8 shows, inserting each tube 28 into an insertion opening 27 of an end plate 26 which is joined to a tank portion 25 to form a header pipe 24 (see Japanese Patent Application Kokai No. 63-105400). With such heat exchangers, heat exchange is made by parallel flows of coolant passing through the flat tubes between the inlet and outlet header pipes.
However, in the arrangement of FIG. 7, it is difficult and time-consuming to form insertion openings on the curved wall of the header pipes for inserting flat tubes, resulting in high unit manufacturing costs.
In the arrangement of FIG. 8, although the two-component structure of the header pipes facilitates the formation of insertion openings on the end plate, this arrangement has a low resistance to the coolant pressure of the junction between the end plate and the tank portion, and the flat end plate must be tightly joined to the outer surface of the tank portion.
In addition, the brazing material tends to flow into the flat tubes, plugging some tubes. There is a demand for a compact condenser for automobile air conditioners.